Amp gauge shunt

[bbab3]

Mattax thanks for your help. Your last diagram makes a lot of sense, the size of the shunt and the guage of wire should not be to hard to figure just by the amount of needle movement. What size shunt would you recommend would you recommend as a starting point using an factory amp guage that has been cleaned and re-soldered?

Have you thought about posting a thread in the how to section? The information I have found to say the least is not clear or just a "band-aid". As you know a large number of members have up-graded to late model Denso alternators and are following the schematics drawn by MAD Electronics and Allpar. The wiring just needs to replaced and the circuitry updated, not just spliced.

 

[Mattax]

What size shunt would you recommend would you recommend as a starting point using an factory amp guage that has been cleaned and re-soldered?

I don't know. There was a guy here whom I was helping figure out his '76. We didn't get far enough to ask the length and wire size on the shunt.
There's a guy who goes by NachoRt74 on Moparts forum. He was asking about the same thing. I'll see if I can find it.
Are Mopar shunts a simply wire or a known resistance wire ? | Moparts Question and Answer | Moparts Forums
Setting up an aftermarket AMP gauge? | Moparts Question and Answer | Moparts Forums

As far as the rest. I just try to help when I think I can. There's a lot of variations on how things were done originally, and even more on how people want to modify. So there's no one size fits all. Makes it difficult, especially when some people want to be spoon fed, others want plug and chug, and my approach is helping people understand enough to figure things out. I've put some stuff on my website, like this Fusible Links in Charging Systems with Ammeter and at some point I'll update and add more.

 

[skykeith]

I have bench tested several A body Mopar ammeters and some of them were marked +/- 40 and some were unmarked. Full scale deflection on all of them was 40 amps and they were surprisingly accurate. The old ammeters depended on current flow to create a magnetic field to move the needle, the ones with a remote shunt, measure the voltage drop across the shunt (in millivolts) to move the needle. Meters are calibrated to work with a specific shunt resistance and changing shunts throws everything out of calibration.
I agree with Crackedback, I don't like ammeters, so I disconnect them and install a small digital voltmeter in the ashtray. Just close the ashtray and everything looks totally stock.
As far as bulkhead terminals go, if you look at the data sheets for any 1/4 inch spade connectors, you'll see they are all rated for a max 40 amps. Why in the world did Mopar design an electrical system limited to 40 amps and then install 60 amp alternators.
I personally connect the alternator to a power stud going direct to the battery and use a Bussman power fuse module direct off the battery with relays powering lights, fans, and anything else I can to keep as much power out of the car as possible. The less power you run through the bulkhead connector, the more your car will love you for it.

 

[bbab3]

I understand. As posted earlier my big personal fear is an electrical fire. I have seen some major electrical problems over the years and always try to over engineer especially electrical components. Thanks again.

 

[Mike69cuda]

Mattax, I have really learned a lot from your posts. I have been a career electrical guy, but not in the automotive business. There is a lot of subtlety to the old Mopar electrical systems that would probably take me more years than I have left to figure out on my own. I did a lot of this back in the day when I had these cars in my youth. Was pretty much out of it till 4-5 years ago when gearhead son got to driving age. This forum has been a great help to me since I bought my cuda. I have particularly enjoyed your work. I hope I can contribute as well as time goes along.

 

[bbab3]

I currently have the dash on my work bench and just finished painting the dash fascia and installed new inlays. Now concentrating on the electrical. I am installing a new solid state IVR and re-soldering connections. I know the factory harness needs some help especially due to the electrical system changes resulting in the alternator upgrade. As for the amp guage it was ether re-solder it's connections and test, or install the guts of a Sun Pro volt guage in the ralley amp gauge housing. The shunts and heavy guage wiring worked on my Power Wagon, and I did not baby it. Just trying to explore my options. Considering I need to replace the charging circuit, keeping the amp guage seems the best.

 

[AJ/FormS]

Didn't read the whole thread
The factory Ammeter has a good sized shunt already built into it. I was impressed when I saw it.
The biggest issue is the ancient bulkhead connector; get rid of it. Wire every non-factory accessory, and the headlights, on relays and forget all about your troubles. After I did that in year 2000, I have never had another scary stinky-plastic trip again,worrying if my car is gonna catch fire. I was nearly 70 miles from home the first time I smelled it. I pulled over right there, waited for the engine to cool, and punched thru the melted plastic with a temporary repair,which I made permanent after the trip.
I carry an emergency repair tool kit. You pretty much have to with a 50 year old car, cuz you just never know......
On another car I had to make a fusible link bypass on the side of the hiway, this time on a cold winter day, on my way to work. I had to rob other, non-essential, wiring to get moving. Never leave home without a length of wire and a wire cutter; there are legitimate reasons that some of our cars come to us with hacked harnesses.
On another car I had to replace a magnetic pick-up, this time only 25 miles from home; and in summer,yahoo!
Or a factory ECU. Or numerous Ballast resistors over the years, there is no prophesying when one of those will just give up. And tail-lights; you gotta stay on top of those, cuz 3 minutes after you lose one, your muscle car will be pulled over and the cop will give you a twenty-minute safety lecture!

 

[Mattax]

Mattax, I have really learned a lot from your posts. I have been a career electrical guy, but not in the automotive business. There is a lot of subtlety to the old Mopar electrical systems that would probably take me more years than I have left to figure out on my own. I did a lot of this back in the day when I had these cars in my youth. Was pretty much out of it till 4-5 years ago when gearhead son got to driving age. This forum has been a great help to me since I bought my cuda. I have particularly enjoyed your work. I hope I can contribute as well as time goes along.

Thanks Mike. I've learned a lot from others here and at Moparts. Nacho in particular got me headed on the right path, although his English can be challenging. LOL. When he opened up and repaired a couple failed ECUs - that was a clue he had a decent understanding and curiosity of how electric and electronics work.

electrical system changes resulting in the alternator upgrade.

Its really more about the loads. If the lights draw 10 amps, then it doesn't matter if the alternator is capable of putting out 15 amps or 150 amps, only 10 amps will flow through the wires. You're adding extra electrical loads over the factory options; so that's why the wires and connectors will carry more current, for longer times, than in the original design.

The challenge is finding an alternator and pulley combo to produce enough power at idle speed that the battery doesn't have to lend a hand. Because if the battery has to help, then it will also need to be recharged. The more this happens, the more the charge circuit has to carry current. Going with a Denso or something like that is definately a better starting point than an early Chrysler design for what you are planning. Just make sure any 'high output' claims weren't made at the expense of performance at low rpm.

 

[RedFish]

As for the amp guage it was ether re-solder it's connections and test, or install the guts of a Sun Pro volt guage in the ralley amp gauge housing.

You'll find there are no solder joints in the amp gauge. It's splined contact studs were simply pressed through the shunt. The 3 pieces are in some very hard plastic.
One downfall in the rally dash is having this firecracker hot gauge in the same cluster with any gauge that has a chassis ground path. That is the fuel gauge. Even the needle of the amp gauge is hot. If/when the black matting piece would break loose and fall against the gauges, 12 volts would go through the fuel gauge. It's needle would disappear to ash in a flash. I can't know how many times this happened but I do have 2 examples here, rally fuel gauges with burnt nubs where the needles once were. Rule #1 Don't tap on the glass. LOL
Since you are installing a remote solid state instrument voltage regulator, do block the back of your fuel gauge from chassis ground regardless what else you do.

 

[bbab3]

Redfish, the link below is what I read about re-soldering a mopar amp guage.

Bullet-Proof Your Ammeter (A 'How To') - DodgeTalk : Dodge Car Forums, Dodge Truck Forums and Ram Forums

I have not had the opportunity to look at a spare ralley guage I have to see if that repair is feasible. Trying to use the amp guage has its risks versus a volt guage. I looks that no matter what I will be dissecting more than one guage, nothing is easy. The volt guage looks like a much simpler and safer way to go.

 

[67Dart273]

To add or confirm what others have said:

Regardless of what bulkhead type terminals are claimed to be rated at, I've replaced many in electric furnaces that failed at nominal 20A. They simply do not hold up

The ammeter can and WILL melt. The photo from the MAD article says it all. Seen a few of those look exactly that way. It's cause partly by the mounting scheme, meaning the nuts clamp the whole sandwich together IN PLASTIC

The bulkhead connector failed AND the ammeter started to melt way back when on my 70RR. Drilled out the bulkhead terminals and ran "big" wire through there, and rebuilt the ammeter. I caught it in time to repair it Don't remember I was likely "warned" by the smell of hot plastic. I may have reaced under there and "felt the heat."

If you insist on beefing the ammeter for larger full current don't get concerned with "accuracy" You need to know "if it changes" and that "zero" is fairly accurate. You really don't care if it's reading 30, 50, or 100A (My beat up old FJ40 had a large frame Mopar alternator for awhile, the SW gauge was 100A and it would BURY that needle after winching operation)

I still think if you insist on an ammeter (I like them but do without) you should look into building a replacement external shunt meter and do away with the "full current" one. You can do just like Ford/ GM/ Mopar did with external shunt...........use the harness itself for the shunt.

 

[Mattax]

A really good point to emphasize. The battery charging is a big variable. We've talked about this in another thread recently so I wont repeat here. I think the best way to plan the best circuitry for the situation is to add up the known loads (amps) when the engine is running, as well as the loads when the engine is off. Then figure the range of charging load - if its going to be deep cycled - make sure it can handle that.

Here's maybe a better example of that previous diagram with an auxilery fusebox in the engine bay.
IF the equipment fed from that box (fans and lights) are only going to be run when the engine is running, then placing it on the alternator output has two advantages.
1. Avoids sending the power to the fuse box through a fusible link.
2. The power is divided three ways. Even if the battery wants a major charge, at least its on seperate wire.

Here's an illustration of power flow with alternator off, battery supplying fans. Now if the there's an electric fuel pump or stereo, you can draw that in. Point is, the best way to distribute varies on what you're adding and when it will be running.

Recharge will be over the same wires, except in the other direction. So the wires may already be warm, and then they will see a frequently see higher recharge current than stock because the battery was drained more than stock.
Adding a wire between alternator output and the starter relay stud would shorten the path to the fans when running on battery. And, as in the previous example, it would split up the alternator output current.

 

[Mike69cuda]

Guys, on the use of a shunt in an ampmeter replacement application, what would you use for a meter? Would you use a standard 50 / 100 millivolt aftermarket meter mounted under the dash, or could the OEM meter in the dash be modified to work with the commercially available shunts?

I have always had a distaste for some of the engineering (or lack there of) in many GM cars and would hate to use such a shoddy design as using the wiring harness as the shunt resitance to measure current in a decent car.

 

[g413]

In this age of electronics, why couldn't you use a clamp-on DC current sensor to measure the amps and then amplify the output to power a gauge needle. I'm not sure I could do it, but it doesn't seem like rocket science -- and good bye shunt resistor. This wouldn't cost very much and it is quite possible someone has already done this.

To answer the question below: They do make donut-type sensors to measure DC current. I'm not sure if they make the clamp-on (or split-core) type.

 

[Mike69cuda]

Aren’t all the clamp amp meters ac only? Like a transformer, the field has to be changing to induce a voltage in a secondary winding.

 

[Ironracer]

What you need to experiment with this is some type of "big" resistor and test meter such as a starter/ battery "carbon pile" tester or a dual meter starter/ battery/ alternator tester. You can find them on C/L often fairly cheap. I have I forget, sun or snap-on, had bad push button (latching) switches. I simply hard wired it to read voltage and current and "there it is" LOL

I'm confused about this whole thing...

 

[Mattax]

I'm confused about this whole thing...

@bbab3 wanted to use an ammeter with a beefed up shunt. One option was to do it like he did his powerwagon, and the other was to make a remote shunt. 67dart273 was answering the question of how to check the effect on calibration.

However skykeith is correct that the connecting plate in these ammeters (A-body 'til '75) work differently than a remote shunt.

The old ammeters depended on current flow to create a magnetic field to move the needle, the ones with a remote shunt, measure the voltage drop across the shunt (in millivolts) to move the needle.

Recently someone on the IFSJA forum found a fairly reasonably priced remote shunted ammeter. In case anyone is interested, this is an option to the aircraft and marine ones.
https://www.westach.com/product-page/2c6-3
Although the 100 amp shunt isn't cheap. https://www.westach.com/product-page/237-100

Why in the world did Mopar design an electrical system limited to 40 amps and then install 60 amp alternators.

This I can answer now. It was a bit off topic and I assumed a rhetorical question, but seems like since the thread has been revived its worth addressing.

A. In general, they didn't. Looking through the sales books, pretty much only find '60 amp' rated alternators as an option for fleet buyers, until maybe '73.
For example even the C-bodies, '46 amp' was the highest rated alternator in '68
The 1970 Hamtramck Registry - 1968 Dodge Dealership Data Book - Introduction
The 1970 Hamtramck Registry - 1968 Canadian Fleet Buyers' Informational Manual - Dart
Somewhere around '73 some non-fleet cars got an optional '60 amp' Chrysler alternators when equiped with electric window defrost grids. Those had the main power feeds wired through a grommet.

B. The rating is higher than the expected normal load. Running an alternator at its maximum output for long periods of time (100% duty cycle) can burn things out.

Keep in mind that all alternators produce less power at lower rpm.
Alternator maximum output vs rpm always looks something like this.

This is why the crank to alternator pulley ratio is so important for low rpm performance.

C. Chrysler probably didn't expect or want the battery to be charged at 40 amps or even 30 amps. That could can cook a battery or worse.

One reason for using higher output alternator was to power additional equipment, especially at when idling. So in those cases the extra power being demanded wasn't going through the ammeter. However I recall seeing some reference to a modified or different ammeter that went with a fleet wiring setup. I don't remember where now - maybe in a parts book. We can see from the '68 fleet book that a larger battery was required with the 60 and 65 amp alternators. Probably the reasons for the larger battery were so they wouldn't demand as much recharge and also not get cooked as quickly by high recharge rates. Just guessing on that.

 

[rustytoolss]

View attachment 1715269537 Since I have the flu and have a need to keep myself busy I thought I would elaborate with some crude drawings to better explanation my ideas. The first one "plan a" shows the brass shunts like was used on my Power Wagon plus two insulated terminals to clean things up and eliminate the welded splice.
View attachment 1715269541
"Plan b" above shows the use of an external shunt like Stewart Warners uses with their amp gauges that are rated to 100 and 300amps.

Also here's the link that made me consider keeping the amp guage in my ralley dash.
Bullet-Proof Your Ammeter (A 'How To') - DodgeTalk : Dodge Car Forums, Dodge Truck Forums and Ram Forums
This shows how to improve the conductivity of the guage.

Hope this helps.

Did you ever get your ammeter idea worked out using a shunt across the terminal on back of the gauge ? I have a 62 plymouth, and have installed a 78amp mopar sqquare back alternator. I would like to do something like what you talked about (bridging the posts of the gauge) Can you tell me more about what you did. I don't have a truck ammetter to get shunts from, but thought I could make something..any help would be great.

 

[slantsixdan]

I have be reading a number of threads related to alternator upgrades. The Mad Electronics method of eliminating the amp guage looks good

Strongly unrecommend the hacky "fix" proposed by the MAD Electrical clowns; you can do a much better, safer job of it—see here. Link also contains info on adding an external shunt so you can keep your ammeter but without running high current into/out of the dashboard.